Many high power amplifier monolithic microwave integrated circuits (MMICS) at microwave frequencies use GaAs pHEMT transistors. Under compression these power amplifier MMICs can pull gate current due to break down effects, rectification current, or “kink” effect current. The GaAs pHEMT structure built by many of the GaAs foundaries have an anomaly known as “kink” in the current-voltage curves of the gate of the transistor. This “kink” anomaly, renders difficult operation of a transistor at a particular gate voltage, because the load line of an associated bias circuit may intersect the gate current versus voltage curve at more than one location. Other technologies also exhibit this “kink” effect, including a relatively new technology involving GaN.
Known attempts to address the known “kink” problem include using resistor dividers with significantly higher current levels. This results in a load line for the bias circuit that avoids the kink in the gate current versus voltage curve. A problem with this approach is that it pulls more current from the supply voltage, which is not necessarily desirable. It is also sometimes possible to use a digital to analog converter to set the gate voltage to the power amplifier, but this requires an entire application specific integrated circuit (ASIC) to provide gate bias, which can be costly.
Most attempts to address the current-voltage kink and the impact to device performance focus on material science to try and remove the “kink” anomaly from the transistor. These approaches involve changing the doping profile of the transistor and changing the material structure of the transistor.